"Over 100 embryos may produce one baby, and it can have problems, " said Ryuzo Yanagimachi, a biologist at the University of Hawaii.

CNN: Health - House members open hearings on human cloning

Yanagimachi said he doesn't know why the mice gained weight, since they have the same food intake and same amount of exercise as the non-cloned mice.

CNN: Cloning experts to tell House committee pros, cons

Ryuzo Yanagimachi, a biologist at the University of Hawaii, found that when he cloned a certain strain of mice prone to have diabetes, the clones would look normal at birth, but upon reaching puberty -- which, in mice, is after eight weeks -- they gained weight.

CNN: Cloning experts to tell House committee pros, cons